Cooling of chromium plating solution



United States Patent Lyon Incorporated, Detroit, Mich.,'a corporation of Delaware n Filed Mar. 17, 1958, Ser. No. 722,063

Claims. c1. 62-100 The present invention relates broadly to the art of plating, and is more particularly concerned with a novel method of accomplishing temperature control in chromium and like plating baths.

It is known that during electrolysis of a chromic acid plating solution there is a substantial heat input to the solution, and that a rise in the solution temperature requires a current increase in order to maintain proper plating conditions. Accordingly, it is customary practice in a continuous plating line, in order to maintain the bath at the desired temperature, to pass the heated solution through heat exchange means, and by reduction of solution temperature, assure formation of a chromium deposit having the desired characteristics. r

The cooling fiuidgenerally employed in. the heat exchanger is water from a municipal supply system, and while during the major portion of the year the temperature of the water is normally sufficiently low to provide the desired cooling, in many locations during the summer months the water temperature is such that it performs rather poorly as a coolant. The result is that it has often been necessary under these conditions to shut down the plating line until .sufiiciently cool Water is obtained. While it would appear that a sufiiciently large heat exchanger could be employed, this has not provenexpedientfrom a production standpoint.

Itis therefore an. important aim of the presentto provide a temperature reduction method forplating solutions which is essentiallycontinuousin operation and does not cause substantial interruptions to the plating procedures. I 1f Another object of this invention lies in'the provision of a cooling method for chromium plating solutionswhich solution to the bath, the vapor portion therefrom being condensed and the condensate employed in' connection with the rinsing operation. v v

A still further object of thepresent invention lies in the provision of apparatus for cooling chromium andlike 'plating solutions, comprising a tank containing relatively warm plating solution, evaporator means receiving the relatively warm solution and reducing the temperature of said solution by removing the low temperature vapor portion, and means connecting the tank and evaporator means feeding the relatively warm solution to the evaporator means and returning the relativelycooler solution to the plating tank. I

A still further objectof invention is to provide cooling apparatus of the foregoing character, and which may further include condensing means receiving the'low ice 2 temperature vapor portion of the solution from the evaporator means and passing the condensate to a container for use in connection with the rinsing operation.

Other objects and advantages'of the invention will become more apparent during the course of the following description, particularly when taken in connection with the accompanying drawing.

In the'drawing, wherein like numerals are employed to designate like parts throughout the same:

The single'view illustrates apparatus suitable for practicing the method of the present invention.

Briefly stated, the method of this invention comprises withdrawing from the plating tank a predetermined quantity of relatively warm solution and passing said solution into exaporator means which may be in the form of a vacuum chamber. The solution is caused to boil within the evaporator means to a degree sufiicient to produce a liquid portion of substantially reduced temperature. The lower temperature liquid received from the evaporator means is returned to the plating tank, and in combination ,with the solution present therein, accomplishes a temperature reduction of the entire body of solution to the point desired for optimum plating conditions. The vapor portion produced in the evaporator means is passed to a condenser, and the condensate therefrom withdrawn and directed into a tank which may be employed for rinse or recovery purposes. Liquid in the rinse tank may be flowed into the plating tank to maintain the desired solution level therein.

Prior practice in the art, as has been noted, required shut down of the plating line during certain periods of the year, and in the figure there is illustrated apparatus by means of which this unsatisfactory condition is eliminated, and savings of approximately 55% of the plating solution eflfected. While the structure shown has proven particularly efieotive in recovering substantial quantifies of chromic acid plating solutions and will be described in that connection herein, it will be appreciated that the features of this invention are not restricted to a chromium plating bath and may be utilized with other known plating solutions presenting similar problems of temperature control. I

In accordance with the principles of this invention,

there is located in the tank 10 ofthe figure a feed line 12 to withdraw high temperature plating solution from .said tank. Providedfor the purpose of returning reduced temperature-liquid to the tank is a return line 14. One end of each of the lines 12 and 14 is submerged in the plating solution,'and experience to date has indicated that a depth of between fourteen and eighteen inches is generally satisfactory.

- To provide a positive flow of relatively warmer solution from the tank 10 to evaporator means "16, there 'is preferably located in the line 12 a-feed pump 18' which maybe of the electrically driven centrifuge type.' A similar pump 20 is utilized-in the return line 14'to increase the flow of'cooled liquid from the evaporator 16 equilibrium at approximately F; at a current density of two amperes per square inch and a plating time of six minutes; During electrolysis, however, the temperature of'the plating-solution may 'rise well above 120 F., and 'may be more in the order of F. or more. Cold water from the'm-unicipal supply system is accordingly circulated through cooling coils in the tank; however, in

ini-any regions during the: hot summer months water from the cold tap may reach a temperature of 85 F. and

therefore have rather poor coolant qualities.

To maintain atypical chromiumplating bath at equilibrium with a temperature not substantiallymor than 120 F. under the other conditions noted, relatively warm solution iswithdrawn from the tank through the feed line 12 and evaporated sufiiciently to remove an amount of heat therefromsuch that the cooled liquid returning to the tank through the line 14 will have n temperature generally around 100 to 102 F. Since conditions within the evaporator means 16 may have to be changed under yariations in the temperatures of the :liqui'd'carrie'd by the lines 12 and 14, indicating means 22 and 24 are located in said lines to obtain liquid temperature readings therefrom.

The evaporator means 16 'may take'any one of a number of diife'rent forms known to the art, and one construction which has proven quite effective in actual prac tice is a vacuum chamber of the barometric flash type. The chamber 16 is designed to receive and return a fluid flow of approximately 2200 gallons per hour, and by a reduction of pressure within said chamber, causes a flashoff of low temperature steam to accomplish a temperature reduction of from about 120 F. to approximately 100 F. 'A vacuum pump 26 of proper capacity is in communication with the evaporator chamber 16 to reduce the pressure within sai'd'c'hamber, generally to around 27.5 inches of mercury, to readilyoause boilin 'of'the relatively warm 's'olu'tion supplied thereto. Thus, by utilizing the latent heater vaporization of the plating solution, the desired temperature reduction is accentplished. V 7

steam or va or generated during the boiling process within the evaporationchamber 16 may be received in line 28 extending outwardly from the u per portion of "the chamber and in communicationwith a condenser 30 by passage throughone wall thereof. The condenser 30 may be of any suitable evaporative type, and is refer ably provided interiorly thereof with cooling coils '32 to convert the vapor into a liquid state. Components customarily forming a part'o'fan evaporative condenser, and including such means as a blower motor, spray pump, and the necessary water, thermostatic and drain valves, are associated with the'condenser construction shown. In addition, a temperatureindicating device 34 is normally included 'to obtain steam temperature readings. I

Condensateproduced in the chamber 30'is removed therefrom by a vacuum pump 36 located in the line 38 which terminates in a tank or other-structure 40-providing a-rinse or recovery point for the condensate. The tank 40 is'located in proximity to the plating tank 10, and there is provided a return line 42 having apt'r'mp 44 therein to flow rinse solution to the plating tank to maintain the desired level therein, a's'dete'rminedt by'a level control device. 46 in said tank 10. 'It should be mentioned in this connection that the prior practiced procedure has beento dump the rinse tank solution into-the drain when, a particular concentration of chromic ,acid was found to be present therein. Now, however, .by pumping relatively pure condensate into the rinse tank, .the chromic acid concentration therein is maintained at a sufficiently low point that frequent pumping is .not required. In addition, since a small amount of chromic acid invariably exists in the rinsetank 40, this maybe pumped into the plating bath and used to restorethe liquid level to the desiredpoint, that is, to replace solution taken therefrom on, the work pieces and other such losses. Rinse solution is,thus no longer wasted, and said solution used for a valuable purpose in the plating tank when the.chromic acid concentration in the rinse becomes too high. This however, never reaches a:critical point since the rinse solution is diluted .by condensate H from the line 38. Preferably, the intake for thelinel42' It may be seen from the foregoing that there is pro-" vided by the present invention method and apparatus which effectively maintains the temperature of a plating solution at any level desired. The structure shown may incorporate temperature control and other electrical means to the end that a predetermined increase in the solution temperature in the feed line 12 from the tank will automatically initiate withdrawal of solution and evaporation thereof to accomplish a heat reduction and return of cooled li uid to the tank 10. Each of the contponents of the system are relatively simple in construction and operation, and the plating procedure may continue uninterrupted during the removal of relatively warm solution and return of cooled liquid. Minor additions of chromium trioxide and catalyst may 'be required from time to time to revitalize the plating solution; however, this is customarily accomplished with little interference to the plating operation. v

, Pursuing the p 'nciples of this invention, it is no longer necessary to waste by drainage substantial quantities of rinsing solution, nor to cause potential damage to a sewage system by passage therein of relatively high concentration rinse solution. Further, and probably of prime importance, a close down of the plating operation is no longer necessary as was required when solution temperature could not be broughtdown sufiiciently by earlier heat exchangetechniques. EXperience in actual practice has indicatedthat quantities of plating solution approach- 'ing 5 5 or more percent can be saved by practice 'of the herein disclosed method, and this is particularly true during the warmer months of the year.

I It is to be understood that modifications may be effected in the processes and structures herein disclosed departing from the spirit of the invention or the scope of the subjoined claims.

I claim jas my invention:

1. A method of equalizing the temperature of a plating bath having relatively warm aqueous plating solution therein, which includes the steps of passing the relatively warm solution into an evaporation zone and removing *heat from 'said solution by boiling while generating vapors therefrom to substantially reduce the temperature of the solution, passing the reduced temperature solution directly into the plating bath at essentially the temperature resultin'g from the heat removal in the evaporation zone, removing the vapors from the evaporation zone and directing said vapors into a condensation zone, and removing the condensate from the latter zone and receiving the same'in'a'collection zone.

2 A method of equalizing the temperature of a plating'bath'having'relatively warm aqueous plating solution therein,which includes the steps of passing the relatively warm solution into an evaporation zone and removing heat froin said solution while generating vapors therefrom to substantially reduce the temperature of the solution, passing the reduced temperature solution into the plating bath, removing the vapors from the evaporation zone and directing said vapors into a condensation zone, removing the condensate from the latter zone and receiving the same in a rinse bath, and passing rinse solution from the latter bath into the plating bath to maintain the desired level therein.

'3. Apparatus for cooling plating solutions, comprising atank containing plating solution, a vacuum chamber for boiling said solution to reduce the temperature thereof .and having a solution inlet and outlet and a vapor outlet, tubular means connected to the tankat one end and at their opposite ends to the solution inlet and outlet, means for pumping relatively hot solution from the tank through the tubular means to the chamber, means for pumping relatively cool solution from the chamber, t g he b m n t 'th v ta k) PQf q 'en l tubular means connected to saidcohdenser and the chambe x r g let e e n asl tiqaye s t f the chainber to the condenser, atank normally containing rinse solution, means for removing condensate from the condenser and passing the same to the rinse tank, and means pumping rinse solution from the rinse tank to the plating tank maintaining the desired level in the latter tank.

4. Apparatus for cooling plating solutions, comprising a tank containing aqueous plating solution of relatively high temperature, an evaporation chamber for reducing the temperature of a solution passed therein and provided with a vapor outlet, tubular connecting means between the tank and chamber simultaneously removing relatively high temperature solution from the tank and directing relatively cool solution thereto, a rinse tank communicating with said plating tank, and condenser means communicating with said vapor outlet in the evaporation chamber and with the rinse tank receiving vapor from said chamber, condensing said vapor and directing the condensate to the rinse tank for mixture with the solution therein and transfer to the plating tank to maintain a desired level therein.

5. A method of controlling the temperature of a plating bath, which comprises withdrawing from the bath a quantity of relatively high temperature aqueous plating solution, removing heat from said solution by boiling, separating said solution into aqueous vapor and aqueous liquid solution portions both having a lower temperature than said relatively high temperature aqueous plating solution, removing and condensing the vapor portion, and passing the liquid portion to the plating bath to reduce the temperature thereof, while directing the aqueous condensate first to a rinse bath and then to the plating bath in admixture with rinsing solution.

References Cited in the file of this patent UNITED STATES PATENTS 2,096,147 Toulmin Oct. 19, 1937 2,140,306 Beals Dec. 13, 1938 2,745,798 Haveisen May 15, 1956 2,825,681 Johnston Mar. 4, 1958 

